Well, I just found out that the rear end in my 87 GN is not an 87 GN rear. It is some piece of sh....crap with 2.56 gears. A guy emailed me about a 86 T-Type rear end with 3.42 auburn pro posi. Is this a compatible fit for my car? What other rear ends will work for my car? I want to have a 10 bolt, 8 1/2 rear with 3.42 gears like stock, but I don't know what other regal type cars had this combo. Any advise is appreciated. Also, if you're in the Ohio area with one for sale give me a shout!
Basically you're limited to the turbocharged Regals from 84 up. The Olds 442 from the same years had 3.73s.
The housing is whats hard to get. Hurst OLDS, T-Type and GN only. The Monte SS uses a 7.5. Gears are easy, 3.42 the best.
I have one, email me. jdoino@conaxbuffalo.com
Have to refute Phil's post. Monte SS's came with 8.5 and 8.8's and could be specially ordered with GN rears with 3.73's. Stock the gears in the Monte's varied from 3.42 to 3.73 with 3.55 being the most popular. The one problem with any stock gm ten bolt is the posi unit's are absolute crap and you have about a 25% chance of finding a working posi in a used rear. So if the posi is what your searching for your better off getting a solid rear and and aftermarket posi and spending the weekend in your driveway.
'83-'84 Monte SS got the 7.5" 10 bolt with 3.42 gears. Limited slip was not optional.
'85-'88 got the 7.625" 10 bolt with 3.73 gears. Limited slip was optional.
Those were the only rears and ratio's the SS could be had.
Ditto what Rob said (looking thru the Chassis Manuals and from my experience).
- Monte's all had either the 7.5 or the later ones got the 7.625 (7 5/8").
- The Olds 442 (go figure) got the 8.5 with 3.73 gears.
- Turbo Regals got the 8.5 with 3.42s
Once again I have to disagree. While I'm not saying what your saying is incorrect. According to the paperwork there were the basics for the Monte. But if you know how to look in a boneyard any and all of the above rears were available. GM is known for stuffing what's available under a car when part counts are low. (E.X. 70 LS6 with L89 aluminum heads, although never produced officially, factory records showed 50 going out the door)
Add in the possibility of COPO's (central office production orders) and you find even more strange combinations. Plus let's face it, with GM interchangability there are how many more with rear's stolen from GN's and 442's. Discounting the Monte as a possible place for his parts was unsound advice, knowing your number's while your looking is more important then what your looking under.
And once again to refute false info, 84 limited slip was an option, 83 it wasn't.
http://www.montecarloss.com/SS_FAQ_5.html#7
Just if you wanna check.
I know that on Dec. 31, 1983, you could not order limited slip in an SS. When my Dad and I were at the dealership ordering the car, that was an unavailable option on the SS. A regular Monte could have been ordered with it though.
T-Tops and overdrive weren't available either. As with posi, these were options that he wanted. The only option the car didn't have was the remote passenger mirror.
As an aside, the Monte ended up with a 200r4 and rear out of a GN back in 96. Also got a nice 355. So in the end, it got the big rear with posi, and an overdrive transmission.
I have a new GM 8.5-- 3.73 gear set ordered for 84 Hurst Olds if anybody is interested. I have heard they don't work well in GNs. Found that out after I bought them
Colin, while it's worthwhile to look under any G-body (who know what might be lurking there!
), if you want to play the odds, you won't spend a lot of time looking under the Monte's. It'll be a rare Monte indeed that has something wasn't readily available from the factory. Unless there's something really messed up in the Chassis manuals, they didn't put the 8.5 under the Monte.
Agreed, if your playing the odds, looking under the monte's is not the fastest way to find a rear. But if your already in the boneyard it might be prevalent being as you may only find one or 2 GN's but 15 or 20 montes. So you have more of a shot then running to 8 or nine junkyards looking for a solid rear.
And I never truly trusted the chassis manuals because I have seen way to many GM's with matching numbers and parts that should not have been there. I myself had an 84'ss with a GN 8.5" 3.73 stock. All vin's and purchase orders were original because I bought it from the original owner. The women bought it as an 84 leftover. So how it came to be under the car I have no idea. I just attributed it to either friday night quickie or monday morning hangover at the plant.
OK Colin ... you win.
However, the GNs never came with 3.73s... and that's a fact!
Agreed Like I said, no idea how it got there. Not trying to win or lose, just don't want anyone to miss out on a possible find. Sorry if I seemed combative.
Phil mentioned that the 3.73's were not a good combo for the GN's. Why is this? Is this just a misunderstanding?
The 3.73s are only "not a good combo" if you retain the stock tire heigth ~26". Just adding the gears puts you into the higher RPM band quicker...and with a otherwise stock drivetrain, this has been shown to be of no benefit.
If you go to the 27" or 28" tall tires, 3.73 gears are of benefit IF you want to get back to the original gear/tire heigth ratio.
However, it has been my experience that once a TR has been modified to the low 11's and/or has started running out of RPMs to use in first, seccond and third at the track (fourth isn't a good idea for racing), then by switching to the taller tires - retaining the 3.42s - you can get the motor back into acceptable RPMs.
For a more "all-out" race motor that can run the higher RPMs, taller gears (i.e. the 3.73s) can get you to the higher RPM band(s) more quickly which, presumably with the "all-out" race motors, is where the optimum torque/HP levels are.
Keeping a higher "load" on the turbo is beneficial. This can be accomplished with taller tires or lower ratios rear-ends, within limits of course. On my TSM car, I run 3.73s with 29.5" tall tires.
As I recall, one year Kent Rudbeck was running 3.73s and running X MPH. One day he (accidently) launched in second gear - ET was fairly consistent, but MPH went up by ~2.5. He then put the 3.42s back in, kept the +2.5 MPH and gained nearly two tenths in the quarter. Case and point.
I have a 79 Malibu with a 10 bolt 7.5 inch ring gear,moser axles with c-clip emliminators installed on them. I want to up grade to a 8.5 inch 10 bolt grand national rear end. Will my axles work with the 8.5 10 bolt,I think my alxes a 26 spline. If not how many splines does the GN rear end have. What do I have to do in order for my same axles to work in a GN rear end.
The GN 8.5" uses 28 spline units. Some aftermarket carriers use 30 spline units, and spools are available with 33 splines, as I recall.
I don't think the 7.5" axles will work in an 8.5" rear end.
Scott,
Is the spline count the same [28] for ALL GM 8.5 10 bolt rears?? For ALL years??
Ron
Can I interject a question on the wording you are all throwing around here? I'm going to start doing work on my car soon, an 83 Regal, and one of the targets is the rear end. It's definitely a stock, open rear, but I don't follow the terminology - 10 bolt, 12 bolt, 8.8, I'm totally confused! I can and know how to do the work, just don't understand how to identify it! Thanks for any help
In answer to the question....
The 7.5" rear end was by far the most prevalent rear used in the G-bodies. It refers to the ring gear diameter.
The 8.5" rear end was a (relatively) special rear end used in some G-bodies (primarily the GN and 442) and it is stronger and "beefier".
The number of bolts terminology usually refers to the number of bolts holding the ring gear to the carrier (not the rear end cover as some people have been led to believe over the years).
The 7.5" and 8.5" are both "10 bolts". Chevy had a very tough "12 bolt" that is a totally different rear end. The 8.8" is usually a Ford rear.